1. Field of the Invention
The present invention relates to a zoom lens, an imaging device, and a personal digital assistant.
2. Description of the Related Art
Accompanied with the wide spread of the imaging device represented by a digital camera, the general trend seeks for further improvement of the quality of a photographed image and further downsizing of the body, and it seeks for higher performance compatible with further downsizing of the zoom lens used as a photographing lens.
In view of further downsizing of the zoom lens, first, it is necessary to shorten the total lens length in use (distance from the lens surface on the most object side to the image surface), and it is also important to reduce the thickness of each lens group to thereby shorten the total length in storage.
In view of seeking a higher performance, it is preferable to secure a resolving power equivalent to an imaging element of at least 5 to 8 million pixels, throughout the whole zooming range.
Further, a wider angle of view of the zoom lens is strongly requested, and it is preferable that the half angle of view at the wide angle end is 38 degrees or more corresponding to the focal length 28 mm in conversion to the 35 mm film-based camera (the so-called Leica type). The changing magnification rate is also desired to be as high as possible; provided that the zoom lens has the changing magnification rate corresponding to the focal length 28 to 200 mm in conversion to the 35 mm film-based camera, it is considered as possible to deal with almost all of general photographing.
There are various types of the zoom lenses for the digital camera. As a zoom lens suitable for a higher changing magnification rate, the patent documents: JP-A 2006-113453, JP-A 2006-133632, JP-A2006-235062, and so forth disclose zoom lenses having such a configuration that a first lens group has a positive refracting power, a second lens group has a negative refracting power, and a third lens group has a positive refracting power in order from the object side; and at least the first lens group and the third lens group move toward the object side in changing magnification from the wide angle end toward the telephoto end, in such a manner that a spacing between the first lens group and the second lens group increases and a spacing between the second lens and the third lens decreases, which have a wide angle range 38 degrees or more in the half angle of view or close to it, and have a sufficiently high changing magnification rate over 6.5.
However, the zoom lenses disclosed in the above patent documents embrace the following problems.
In the zoom lens disclosed in the patent document JP-A 2006-113453, the number of the total lenses configuring the zoom lens is as many as 13 to 17, except the example 6 of which half angle of view at the wide angle end is rather small, 26.5 degrees, and the lens configuration is complicated. And, it is difficult to sufficiently meet the demands of recent users in further downsizing, especially, the reduction of the total length in storage, and the reduction of the cost.
In the zoom lens disclosed in the document JP-A 2006-133632, the number of the total lenses is 11, and it is not too many. However, each lens group has a significant thickness, and it is difficult to reduce the total length in storage.
Of the zoom lenses disclosed in the document JP-A 2006-235062, the one disclosed in the fourth embodiment achieves the changing magnification rate 6.5 or more with the number of the total lenses of 10, and the thickness of each lens group is comparably reduced. However, the total lens length at the telephoto end is somewhat long, and the size at the telephoto end as the information device is somewhat large.